Diffusion and Active Transport
Dissolved substances can more into or out of cells by diffustion or active transport.
Water moves into and out of cells by a special type of diffusion called osmosis.
Keeping the body hydrated is important for human health.
Water lost in sweat during exercise must be replaced.
Sports drinks contatin water for hydration, but also glucose for energy and ions to keep the body healthy.
Active Transport moves substances across cell membranes against a concentration gradient.
This require energy and a protein carrier.
As organisms get bigger their surface-area-to-volume ratio gets smaller.
This makes diffusion inefficient.
To solve the problem they develop special exchange surfaces.
All exchange surfaces are thin, have a large surface area, and have systems to maintain a concentration gradient.
The villus is the site of absorption in the small intestine, and is efficiently designed.
Gas exchange vs. Breathing
The lungs are the organs of gas exchange in humans.
Breating is the process which brings air in and out of the lungs.
Transpiration is the loss of water from the leaves of the plant.
Water leaves the plant through tiny pores called stomata on the under surface of the leaf.
Rate of transpiration
The rate of transpiration can be measured by a potometer, and can be affected by a number of environmental factors.
A second problem for larger organisms is that they require a transport system to move substances around the body.
Humans have a circulatory system that involves the heart, blood, and blood vessels.
The heart is a muscular pump that pushes the blood around the body.
Blood passes through the heart twice in one cycle of the body; it is a double circulatory system.
The blood is the fluid that transports substances.
It is composed of a liquid called plasma, and cells - red cells, white cells, and platelets - each with their own function.
Vessels - viens, capillaries and arteries
The blood is circulated in vessels: arteries take blood away from the heart, capillaries take blood through the tissues, where exchange occurs, and veins take blood back to the heart.
Technology - Artifical hearts and blood.
Technology has developed artificial blood for use in transfusions, and stents to open blocked vessels.
Artificial hearts or valves can be used to replace damaged ones.
Plant transport - Xylem and Phloem
Plants also transport substances.
The xylem transports water from roots to the leaves, whilst the phloem transports sugars from the leaf to other parts of the plant.